DHCP stopped working for wired clients (possibly due to new Windows 8 machine on network?)

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Level 1

18 points

DHCP stopped working for wired clients (possibly due to new Windows 8 machine on network?)

My home office network has always been rock solid but has suddenly stopped allocating DHCP addresses to wired clients (wireless still works). The only thing that has changed has been the introduction of 2 Windows 8.1 laptops for my children over Christmas, and I wonder if these are the cause?

My network set-up is as follows...

I have a fibre broadband connection into the home office which plugs into my Airport Extremes WAN port. I then have a single ethernet cable going from one of the LAN ports on the AE to a gigabit ethernet hub, into which I have 10+ machines. The AE is set to use PPPoE to get the net connection and the network setting is to use DHCP to sign addresses. The IP addresses are assigned to the wired clients, plus a couple of airport expresses, and a number of iPhones, iPads etc. This has all worked fine for a couple of years, and any device just gets an address and works.

At Christmas both my children got Windows 8 laptops (don't ask!). I connected them to the wifi network (served by the Airport Extreme) and they got assigned an IP address correctly. They can browse fine, and also auto-updated to 8.1 at the same time.

I wasn't working in the home office at that time but did notice a few things not connecting and when I did check, none of the wired devices was receiving an IP address. They all come up as self-assigned. Nothing has changed on the network itself, the cables are still plugged in (the machines haven't moved!). I think somewhere on the network a second DHCP server is running, but I cannot see where. The only new thing are the Windows 8 laptops. Could they be the problem?

Posted on Jan 6, 2015 3:23 PM

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Answer 1

geo_head

Level 1

8 points

Jun 21, 2017 4:34 PM in response to donhertz

I have EXACTLY the same issue except I do not have windows machines on my network. Everything was working perfectly in the morning when I went to work (and had been stable for a couple years) then suddenly nothing on the wired part of my LAN worked though everything on the WIFI works. Everything on the WIFI is getting a NAT IP address and nothing on the wired part of my LAN is getting an IP address.

I've done all the troubleshooting above and more. Nothing works. Any help appreciated!

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Answer 2

Bob Timmons

Level 10

185,108 points

Jun 21, 2017 5:13 PM in response to geo_head

I've done all the troubleshooting above and more. Nothing works.

After restarting the AirPort Extreme, if you cannot get a valid connection by connecting an Ethernet device directly to the AirPort Extreme using a short spare Ethernet cable as a test, then try the other ports.

If all ports are not working, the Ethernet switch built into the AirPort has failed.

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Answer 3

Jan 6, 2015 3:54 PM in response to Matt Carey1

It would seem unlikely for a windows client to introduce a dhcp server.. or to block your wired devices.. still, strange stuff happens.

Double check the setup of the airport extreme.

At the very least reboot the network.. AE and Switch. Then use the airport utility in say iOS to discover if the network has gone bad.

Turn off the two windows laptops and reboot the network again.. does everything then start working.. ?? Power on the laptops does it stop again??

Repeatable experiments are the nature of science.. everything else is voodoo..

See if you can reproduce the problem.

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Answer 4

Bob Timmons

Level 10

185,108 points

Jan 6, 2015 3:56 PM in response to Matt Carey1

Power down the AirPort Extreme

Temporarily, disconnect the Ethernet cable from the LAN port on the AirPort Extreme that connects to the Ethernet switch

Using a short, spare Ethernet cable....any length will do....connect from one of the LAN ports on the AirPort Extreme to a computer. Make sure that the wireless is turned off on the computer, and then check to see if you can get a good Internet connection that way.

If you can, you now know that the LAN port is working correctly (and the Ethernet cable is as well). More troubleshooting will be required to find the issue.

If you cannot get a good Internet connection, then try one of the other LAN ports on the AirPort Extreme.

Post back on your results.

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Answer 5

Matt Carey1 Author

Level 1

18 points

Jan 7, 2015 5:58 AM in response to Bob Timmons

I've managed to spend some time testing and here is what I found out.

Before doing anything I turned off the two PC laptops to make sure they were not available

I powered down the Airport Extreme and disconnected the ethernet cable in the LAN port

I powered on the Airport Extreme

I then connected my laptop (running 10.10) via a single ethernet cable to one of the LAN ports. The laptop had wifi off.

I checked the network control panel, and I had a valid IP address via DHCP. I checked a couple of websites and was able to view them.

I then unplugged the ethernet cable from my laptop and plugged it into my ethernet switch (keeping the there end in the same LAN port on the AE). No machine on the network was able to get an IP address via DHCP, they all came up self-assigned.

I then unplugged the ethernet cable from the AE LAN port. I unplugged one of the cables from the switch that goes to a second switch on the network and plugged that into the same AE LAN port. All the machines connected to that switch came up self-assigned and won't get an IP address via DHCP.

In summary, if a single machine is wired to the AE it gets a valid IP address via DHCP. If multiple machines are connected they don't.

With the Windows machines turned off, I now thinking they might not be the cause. BUT nothing has changed on the network to make this happen.

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Answer 6

Bob Timmons

Level 10

185,108 points

Jan 7, 2015 6:15 AM in response to Matt Carey1

The AirPort Extreme is operating correctly, since you have verified that you can get a good Internet connection when you connect directly to the AirPort Extreme.

So the next step would be to connect the switch to the AirPort Extreme, and disconnect all of the Ethernet devices that are connected to the switch. With a computer or laptop (wireless off on the computer), check each port on the switch one at a time.

If the switch is operating correctly, you will be able to get a good connection at each port. If you find that some ports work and others don't.....then you need to replace the switch. Likewise, if none of the ports work, the Ethernet switch will need to be replaced.

Once you have verified that all ports are working on the switch, then you can connect devices back to the switch and test each device.

In other words, you have to get everything working on the first switch before you can move further and check the second switch in the same manner.

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Answer 7

Matt Carey1 Author

Level 1

18 points

Jan 7, 2015 6:21 AM in response to Bob Timmons

Thanks for taking the time to reply. Useful, and I'll try that.

I unplugged one of the cables from the switch that goes to a second switch on the network and plugged that into the same AE LAN port. All the machines connected to that switch came up self-assigned and won't get an IP address via DHCP.

I did this, as noted above, to test if the main switch was faulty. The main switch has some machines connected directly to it, plus 2 5 port switches, with more machines connected to those. Even connecting one of those 5 port switches directly to the AE didn't work.

But I'll try going port by port, then machine by machine.

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Answer 8

Bob Timmons

Level 10

185,108 points

Jan 7, 2015 6:28 AM in response to Matt Carey1

I'll try going port by port, then machine by machine.

Unforunately, that is the only way that you can find out where the issue might be.

If you suspect that the DHCP server in the AirPort Extreme is not working correctly, temporarily connect 3 Ethernet devices directly to the 3 LAN ports on the AirPort Extreme. If all 3 work, then you know that the AirPort Extreme is providing multiple iP addresses correctly.

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